30
River and Stream Sediments
tes that they are attacking only the non-detrital part of the sediment. With iron, 4.0 N
nitric acid plus 0.7 N hydrochloric acid provides results nearly identical to the total
extraction. For aluminium a different distribution is obtained with considerable
attack on the silicate lattice.
As for the trace elements, the total and 4.0 N nitric acid plus 0.7 N hydrochloric acid
extraction methods give different distributions to the weak extraction methods, expecially for chromium and cobalt. They also show anomalous metal levels at locations
where the weaker methods show only background levels. This is an indication of
variations in the rock matrix of the area and attack of the detrital phase of the
sediment by both of these methods.
The above discussion showed that the three weaker extraction methods satisfy the
essential requirement of minimal attack on the silicate detrital lattice. The remaining
essential requirements are liberation of the metals in question from organic matter,
satisfactory simultaneous extraction of the metals in question from the nondetrital
phases in the sediment, and a high contrast of anomalous to background samples.
Chester and Hughes [46] found a solution of 1 N hydroxylamine hydrochloride and
25 vol. % acetic acid suitable, since this mixture would not attack lattice structures of
clay minerals and reduced manganese oxide phases. Table 2.14 shows that, for most
metals, 0.5 N hydrochloric acid gives higher extraction. However, the levels for manganese were comparable for these two methods, showing that even though 1 N
hydroxylamine hydrochloride plus 25 % acetic acid is a weak extractant, its reducing
character makes it suitable for manganese extraction. The pH of this solution was
found to be 1.5, considerably weaker than that for 0.5 N hydrochloric acid. The
reducing nature of the solution may not liberate organically bound trace elements. A
comparison of the data obtained with 0.05 N EDTA with that of the above reducing
solution shows that there is a significant difference in the amount of copper, manganese and iron extracted. The latter method extracts more manganese and iron, and
less copper. This is satisfactorily explained by the higher acidity and stronger reducing powers of the latter method and the stronger complexing power of the former
method. The pH of the 0.05 N EDTA solution was 4.8, much higher than 1.5 for 1 N
hydroxylamine hydrochloride plus 25 % acetic acid. Thus, the latter method would be
expected to extract more iron. For copper, 1 N hydroxylamine hydrochloride plus
25 % acetic acid gave lowest levels of all methods. It is well known that copper is
highly correlated with organic matter [47,48]. Thus it appears that this method is not
suitable for copper determinations. Holmes et al. [49] used this solution satisfactorily,
to extract zinc and cadmium, and Kronfeld and Navrat [50] used it to extract cadmium, chromium, lead and zinc from the adsorbed phase and the ferromanganese
and carbonate mineral phases of sediments. They stated that this technique does not
dissolve the authigenically formed sulfide minerals or organic complexes. From Table 2.14 this extraction technique is seen to be essentially equivalent to 0.5 N EDTA
except for copper and cobalt.
Chowdhury and Bose [43] have shown that copper complexed with humic compounds isolated from soils is readily liberated with dilute hydrochloric acid (pH 1·0).
Therefore 0.5 N hydrochloric acid liberates copper from organic matter. Thus, unlike
1 N hydroxylamine hydrochloride plus 25 % acetic acid, the above method is suitable
for copper extraction. Table 2.14 shows the mean level of copper with 0.5 N hydro-
River and Stream Sediments
tes that they are attacking only the non-detrital part of the sediment. With iron, 4.0 N
nitric acid plus 0.7 N hydrochloric acid provides results nearly identical to the total
extraction. For aluminium a different distribution is obtained with considerable
attack on the silicate lattice.
As for the trace elements, the total and 4.0 N nitric acid plus 0.7 N hydrochloric acid
extraction methods give different distributions to the weak extraction methods, expecially for chromium and cobalt. They also show anomalous metal levels at locations
where the weaker methods show only background levels. This is an indication of
variations in the rock matrix of the area and attack of the detrital phase of the
sediment by both of these methods.
The above discussion showed that the three weaker extraction methods satisfy the
essential requirement of minimal attack on the silicate detrital lattice. The remaining
essential requirements are liberation of the metals in question from organic matter,
satisfactory simultaneous extraction of the metals in question from the nondetrital
phases in the sediment, and a high contrast of anomalous to background samples.
Chester and Hughes [46] found a solution of 1 N hydroxylamine hydrochloride and
25 vol. % acetic acid suitable, since this mixture would not attack lattice structures of
clay minerals and reduced manganese oxide phases. Table 2.14 shows that, for most
metals, 0.5 N hydrochloric acid gives higher extraction. However, the levels for manganese were comparable for these two methods, showing that even though 1 N
hydroxylamine hydrochloride plus 25 % acetic acid is a weak extractant, its reducing
character makes it suitable for manganese extraction. The pH of this solution was
found to be 1.5, considerably weaker than that for 0.5 N hydrochloric acid. The
reducing nature of the solution may not liberate organically bound trace elements. A
comparison of the data obtained with 0.05 N EDTA with that of the above reducing
solution shows that there is a significant difference in the amount of copper, manganese and iron extracted. The latter method extracts more manganese and iron, and
less copper. This is satisfactorily explained by the higher acidity and stronger reducing powers of the latter method and the stronger complexing power of the former
method. The pH of the 0.05 N EDTA solution was 4.8, much higher than 1.5 for 1 N
hydroxylamine hydrochloride plus 25 % acetic acid. Thus, the latter method would be
expected to extract more iron. For copper, 1 N hydroxylamine hydrochloride plus
25 % acetic acid gave lowest levels of all methods. It is well known that copper is
highly correlated with organic matter [47,48]. Thus it appears that this method is not
suitable for copper determinations. Holmes et al. [49] used this solution satisfactorily,
to extract zinc and cadmium, and Kronfeld and Navrat [50] used it to extract cadmium, chromium, lead and zinc from the adsorbed phase and the ferromanganese
and carbonate mineral phases of sediments. They stated that this technique does not
dissolve the authigenically formed sulfide minerals or organic complexes. From Table 2.14 this extraction technique is seen to be essentially equivalent to 0.5 N EDTA
except for copper and cobalt.
Chowdhury and Bose [43] have shown that copper complexed with humic compounds isolated from soils is readily liberated with dilute hydrochloric acid (pH 1·0).
Therefore 0.5 N hydrochloric acid liberates copper from organic matter. Thus, unlike
1 N hydroxylamine hydrochloride plus 25 % acetic acid, the above method is suitable
for copper extraction. Table 2.14 shows the mean level of copper with 0.5 N hydro-